1. Field of the Invention
This invention relates to dielectric layers with low dielectric constants, and more particularly to forming barriers across exposed pores in porous low dielectric constant dielectric layers.
2. Background of the Invention
Low dielectric constant (“k”) materials are used as interlayer dielectrics in microelectronic devices, such as semiconductor devices, to reduce the resistance-capacitance (“RC”) delay and improve device performance. As device sizes continue to shrink, the dielectric constant of the material between metal lines must also decrease to maintain the improvement. Certain low-k materials have been proposed, including various carbon-containing materials such as organic polymers and carbon-doped oxides. The eventual limit for a dielectric constant is k=1, which is the value for a vacuum.
One of the challenges encountered in microelectronic device processing relates to the diffusion of wet chemical and processes gases through dielectric films leading to increased k values (water has a k value of about 80). While pores left in dielectric thin films after certain process steps may be advantageous from a k-value perspective when dry (dry air or nitrogen having relatively low k values), they may also facilitate fast diffusion of unwanted moisture, and may increase surface reactivity with such moisture due to the increased accessible surface area provided by pores, along with possible hydrophilic SiOH formation to propagate such a problem. SiOH available to react near the surface of dielectric pores may result in an increased k value. Pores may also cause additional challenges to subsequent process steps due to geometric considerations. For example, forming a thin sidewall upon a trench cut into a highly porous dielectric material presents obvious challenge—particularly if one of the sides of the trench upon which a sidewall is to be formed lies in the middle of a large pore.